Biocontrol potential of a newly isolated Streptomyces sp. HSL-9B from mangrove forest on postharvest anthracnose of mango fruit caused by Colletotrichum gloeosporioides

Mango is an important tropical fruit in the world. Mango anthracnose is one of the most severe postharvest diseases caused by Colletotrichum gloeosporioides. Biocontrol by actinomycetes is considered as a promising strategy. Here, 67 actinomycetes were isolated from mangrove forest soils. A strain labelled with HSL-9B showed 63.21% of the inhibition ratio against C. gloeosporioides and broad-spectrum antifungal activities against the selected seven postharvest pathogens. The strain was assigned to Streptomyces malaysiensis based on the phenotypic, biochemical and whole-genomic profiles. Strain HSL-9B extracts significantly reduced the disease severity of mango anthracnose in vivo. 8 × EC50 of extracts completely inhibited the infection of pathogen during the entire storage process. Total soluble sugar contents on harvested mangoes were effectively kept. 4 × EC50 of extracts obviously inhibited spore germination and mycelial growth of C. gloeosporioides, resulting in mycelial rupture and cell ultrastructure destroying. The biosynthesis gene clusters (BGC) of secondary metabolites involved in antagonism were identified by compared with the whole-genome sequencing of strain HSL-9B. Fifteen compounds in strain HSL-9B extracts were obtained using the gas chromatography-mass spectrometry (GC-MS). 12-methyl-tridecanoic acid was one of dominant compounds identified in extracts. Hence, S. malaysiensis HSL-9B is an important bioresource for exploring novel natural products to manage postharvest disease.